The city of Biloxi, Miss., opened itself up to online mockery by marking Martin Luther King Jr. Day as "Great Americans Day."

When it comes to mistakes, Twitter doesn't miss much. The city of Biloxi, Miss., noted that Monday, Jan. 16, was "Great Americans Day." The rest of the country calls it "Martin Luther King Jr. Day." The mess started up because the state recognizes the birthday of Confederate Gen. Robert E. Lee on the same day. Twitter had none of it, prompting the city's mayor to go online to explain what happened.

>>>Click through the gallery to see the city's initial post and the reaction from Twitter users.